Bites and marks on skin

How to examine it

1. Stop trying to read the marks. This page exists because that approach does not work, and the time is better spent on the environment.
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3. Look for evidence rather than insects — dark ink-like fecal spotting, pale smooth shed skins, or bristly husks are all easier to find than a live insect.
4. Check pets and their bedding, and comb for flea dirt, which turns reddish-brown when wetted on white paper.
5. If a tick is attached, keep it after removal in a sealed container. Species affects which illnesses are plausible.
6. Photograph anything you find in place before collecting it.

What else gets mistaken for this

• Contact dermatitis from a new detergent, fabric softener, soap, or plant, which frequently appears overnight and in the areas clothing touches — the same distribution people read as bites.
• Eczema and dry-skin flare-ups, which are seasonal and worsen in heated indoor air in winter.
• Hives from a food, medication, or stress response, which move around the body over hours in a way bites do not.
• Folliculitis and ingrown hairs, particularly after shaving or in areas of friction.
• Scabies, which is a mite but is diagnosed and treated medically rather than as a household pest problem, and which no amount of pest treatment will resolve.
• Fibreglass and insulation fibre irritation after work in a loft or crawl space, which produces intense itching with small red points and no insect involved at all.

What this evidence cannot tell you

Marks on skin cannot establish what caused them, and this is the single most important limit on the site. Reactions vary enormously between people, the same insect produces different marks on different individuals, timing of the reaction differs, and a great many non-bite conditions look identical. A "bite identification chart" is not supportable. Where you see one presented as diagnostic, treat that as information about the source rather than about your skin. The corollary is more useful than it sounds: if you have marks and can find no physical evidence anywhere in the environment, that is itself a finding. Many skin complaints attributed to insects turn out to have another cause entirely, and a dermatologist is better placed than a pest control company to work that out.

What to do with what you found

If a reaction is spreading, blistering, becoming infected, or comes with fever, swelling of the face or throat, or difficulty breathing, that needs medical attention now rather than further investigation. The same applies to any suspected reaction in someone with a known sting allergy. Otherwise, work the environment. Physical evidence — fecal spotting, shed skins, live insects, an attached tick — is what identifies a cause. If you find something, keep it; a specimen is far more useful than a photograph, and your county extension service will frequently identify it at no cost.

Common mistakes

• Buying a whole-property treatment on the strength of a rash, with no physical evidence found anywhere.
• Assuming a pattern of three marks means bed bugs. That pattern is folklore, not diagnosis.
• Assuming a necrotic wound means a recluse spider. Most such wounds turn out to be something else, frequently an infection, and the misattribution delays correct treatment.
• Discarding a tick after removal, which throws away the one piece of information a clinician can actually use.
• Delaying medical attention for a spreading or systemic reaction while trying to identify an insect.

Not sure?

Your county extension service will often identify a specimen at no cost, and that is more useful than a confident guess.

Start the identification key